Employees altered inspection certificates to meet specifications, setting off a rush by Toyota, Boeing and others to see if they had used the raw materials.
TOKYO — For decades, Japanese manufacturers of cars, aircraft and bullet trains have relied on Kobe Steel to provide raw materials for their products, making the steel maker a crucial, if largely invisible, pillar of the economy.
Now, Kobe Steel has acknowledged falsifying data about the quality of aluminum and copper it sold, setting off a scandal that is reverberating through Japan and beyond, and casting a new shadow over the country’s reputation for precision manufacturing, a mainstay of its economy.
Companies ranging from the automakers Toyota Motor and Honda Motor to aircraft companies like Boeing and Mitsubishi Heavy Industry said they were investigating the use of rolled aluminum and other materials from Kobe in their products. They also said they were trying to determine if substandard materials had been used in their products, and if so, whether they presented safety hazards.
Kobe Steel said on Sunday that employees at four of its factories had altered inspection certificates on aluminum and copper products from September 2016 to August this year. The changes, it said, made it look as if the products met manufacturing specifications required by customers — including for vital qualities like tensile strength — when they did not.
Kobe Steel added that it was examining other possible episodes of data falsification going back 10 years. It did not provide details about the size of the discrepancies it had discovered, making it difficult to immediately determine if they posed a safety threat.
The company’s share price plunged more than 20 percent on Tuesday, the first day of trading after a holiday.
No deaths or safety incidents have been attributed to Kobe Steel, but the scandal hits a tender spot for Japan, which relies on its reputation for quality manufacturing while places like China offer cheaper alternatives.
“The falsification problem has become an issue that could destroy international faith in Japanese manufacturing,” the Japanese financial newspaper Nikkei said in an article on Tuesday.
Last week, Nissan Motor said unqualified staff members had carried out inspections at its factories, prompting it to recall 1.2 million vehicles, though it was not clear if the quality of the vehicles had been affected. Mitsubishi Motors and Suzuki Motor both admitted last year that they had been exaggerating the fuel economy of their vehicles by cheating on tests.
Perhaps the biggest blow to Japan’s reputation for quality has come from Takata, the automotive airbag maker that declared bankruptcy in June after causing the largest auto safety recall in history, involving tens of millions of vehicles.
